This cylinder head should work: Cylinder Head
For the nub: hGood DIY Nub Guide
Hopup chamber: Hopup Chamber
Personally I would recommend doing a tdc mod.
For the inner barrel spacers you can just diy them out of tape.
8. I've heard of a mod where you stick the two up chamber arms together (I'm not sure why or what the outcome would be ???)
The Stock hopup chamber has 2 arms. This is theoretically so you can adjust left/right curving. In reality this is kinda bad. It is more convenient to simply stick the 2 arms together. This remains a poor solution since you still have to adjust both screws.
M160 you mean? This might be a little overpowered for the UK-
I assume you are here. I use an m150 in my VSR. In case you did not know, the number tells you the M/S that the BB goes (theoretically) , and no site will let you play with over 500 fps.
You may want to trim the spring slightly- though I would chrono the gun before trying this just in case it is going at the appropriate FPS anyway.